Why houses change with the time and place of birth, which house systems the app uses, and what's left out without a birth time.
Houses divide the sky into 12 sections, based on the time and place of birth. So even people born on the same day get different houses if the time or place differs.
Ways to divide the houses
Placidus
A way of dividing the sky into 12 houses based on time. It's the most widely used system in Western astrology. It can't divide the sky at very high latitudes.
Equal houses
Starting from the Ascendant, the sky is divided into 12 equal houses of 30° each. It's used as a fallback when other systems can't divide the sky.
Porphyry houses
Each space between the four angles is split into three equal parts. It's used instead of Placidus at high latitudes where Placidus can't work.
Whole Sign houses
The whole sign holding the Ascendant becomes the 1st house, the next sign the 2nd, and so on. One sign equals one house, so it's simple. It's used in Vedic astrology and annual profections.
The birth chart and most reports use Placidus by default. At high latitudes (above 66°), where Placidus can't divide the sky, the app switches to Porphyry or Whole Sign, and Solar Return switches to Equal houses. Vedic astrology and annual profections use Whole Sign.
Return charts and location
For Solar Return you pick the city you'll be in around your birthday, and the Ascendant and houses are set for that city. Lunar Return uses the home city in your profile (or your birthplace if none), and your birthplace when overlaying the birth chart. That's because, at the same moment, a different place gives a different Ascendant and houses.
What's left out without a birth time
Without a birth time, the app places the planets at noon that day and leaves out anything that depends on the time.
Ascendant and houses
Not used. The chart is read through signs and planets instead of houses.
Midheaven, IC and angular planets
Not used.
Part of Fortune, Vertex and sect
Not used.
The Moon
Placed at its noon position. If the Moon is within 7° of a sign boundary, the app tells you it might be in the other sign.